Polyolefin compositions and their preparation



United States Patent 3,432,514 POLYOLEFIN COMPOSITIONS AND THEIR PREPARATION George O. Cash, Jr. and Frederick B. Joyner, Kingsport,

Tenn., assignors to Eastman Kodak Company,

Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 16, 1966, Ser. No. 534,636 U.S. Cl. 26093.7 6 Claims Int. Cl. C08f 47/00, 29/02, J/88 ABSTRACT OF THE DISCLOSURE Poly-alpha-olefin compositions having an improved crystalline structure with improved physical and optical properties are obtained by employing as crystallinity promoters a combination of certain metal alkoxides and certain organic carboxylic acids.

This application is a continuation-in-part of our application Ser. No. 405,586, filed Oct. 21, 1964.

This invention also relates to new poly-alpha-olefin compositions having improved crystalline structure resulting in greater clarity and improvements in other physical properties. 'In particular, this invention involves certain new crystallization promoters for accomplishing the foregoing.

As is already known in the industry, when a crystallizable polymer such as polyethylene or polypropylene cools from a melt, crystallization occurs. The rate of development of crystallinity is determined by the rate of formation of crystallization centers and the rate of growth of nuclei. The size of the crystallites depends on the rate of crystallization which depends in turn on the cooling rate and the number of nucleating particles present. Slow cooling and few nuclei favor the growth of relatively large crystallites. When light is passed through a specimen of such a polymer it becomes dispersed as it is reflected and refracted by sphenilites (aggregates of crystallites) within the polymer. The polymer therefore appears white or translucent depending on the thickness of the specimen. If the polymer is quenched from the melt, rapid crystallization occurs with the formation of spherulites of such small dimensions that they do not interfere greatly with the passage of visible light. Such a quenched polymer, however, may have a low degree of crystallinity which deleteriously affects mechanical properties. If allowed to crystallize significantly, the spherulites grow in size and the polymer may lose its transparency.

in certain prior patents and publications, it has been proposed to promote relatively rapid crystallization to achieve small spherulite size and to provide high degrees of crystallization by the use of heterogeneous nucleating agents. For example, the crystallization rates of polyethylene and polypropylene have been increased by heterogeneous nucleating agents such as the metal salts of carboxylic and sulfonic acids. The rapid and high degree of crystallization induced by these prior art nucleating a'gents generally results in improved transparency of the polymer and improved mechanical properties. However, these prior art nucleating agents are difficult to disperse in the polymers and in some cases cause pigmentation rather than an improvement in polymer clarity.

In our parent application aforesaid we have disclosed nucleated polyolefin compositions which we believe represent an advance in the art. Based on extensive further investigations we have now discovered a new binary crystallization promoter which may be incorporated in polyolefin compositions in certain ways more readily and gives products with properties considerably improved over those heretofore obtainable.

3,432,514 Patented Mar. 11, 1969 This invention has for one object to provide new crystallization promoter combinations for improving the transparency and the like properties of crystallizable poly-alpha-olefins. Another object is to provide new crystallization promoters of the type indicated which can readily be dispersed in the poly-alpha-olefins to give substantially homogeneous formulations. Still another object is to provide new crystallization promoters for accelerating the crystallization of poly-alpha-olefins and reducing the size of spherulites while providing high degrees of crystallinity. Still another object is to provide new polyalpha-olefin compositions having a high degree of crys tallinity, excellent homogeneity, and improved clarity and other desirable properties. A particular object is to teach a special combination of a nematogenic carboxylic acid and a metal alkoxide uniquely useful for incorporating in polyolefin compositions. Other objects will appear hereinafter.

In the broader aspects of our invention we have found that a combination of a nematogenic carboxylic acid and a metal alkoxide, both showing transitions within a preferred temperature range correlated to the polyolefin composition to be treated is highly effective in promoting the crystallization of polypropylene and propylene copolymers. Excellent dispersions may be obtained when separate components of the binary crystallization promoter are blended separately into the polypropylene or other polyolefin.

In addition to polyolefinic compositions thus treated having excellent transparency, such nucleated compositions exhibit outstanding physical properties and excell nt color. The alkoxides and the acids of this invention, unlike the metal salts referred to in the prior art, are readily dispersed in the polyolefin by means of conventional techniques to give substantially homogeneous blends and can be used in high concentrations without pigmentation. In addition, the new crystallization promoter combinations of this invention are much more effective than the prior art heterogeneous nucleating agents in providing polyolefins with improved mechanical properties and transparency.

As may be observed (from a study of the prior art, prior art nucleating agents are crystalline, high melting solids which usually promote heterogeneous nucleation through epitaxy. Epitaxy is the oriented growth of one crystalline substance on a substrate of a different crystalline substance. Hence, in order to be effective, the prior art nucleating agents had to be infusible or had to crystallize at a temperature well above the crystallization temperature of the polymer to be nucleated. In contrast thereto, the crystallization promoter combinations of this invention crystallize at temperatures below the melting point of the polyolefins in which they are effectively incorporated.

The alkoxides particularly useful in the practice of this invention are ones which would be fusible at least at the processing temperature of the polymer in question and may be represented by the following general structural formulas:

Since non-fusible metal alkoxides may also be represented by these formulas, the specification of fusibility as above set forth at processing temperatures is significant. In our fusible alkoxides M represents a metal with a valance of a, which can have values from 1 to 6 and M represents a metal with a valence of b, which can have a value of 1, 2 or 3; R represents an alkyl or an aralkyl group containing 1-12 carbon atoms and n is l, 2, or 3.

The carboxylic acids useful in the crystallization promoters of this invention are qualified by three aspects:

(1) They preferably exhibit a nematic mesophase below the melting point of the polyolefin;

(2) They should be compatible with the polyolefin (that is, they do not of themselves deleteriously affect the clarity of the plastic); and

The alkoxide-acid crystallization promoters of this invention are especially useful for improving the properties of polypropylene and the crystallizable copolymers of propylene with ethylene and with other alpha-olefins. In general, however, crystallizable polymers and copolymers (3) They should be reasonably stable at the processing 5 of alpha-olefins containing from 2 to carbon atoms can temperatures of the polyolefin. be used. Some examples are polypropylene, ethylene/ Our preferred acids may be represented by the followpropylene block copolymers, polybutenes-l, propylene/ ing general formulas which are intended to illustrate and butene-l copolymers, propylene/hexene-1 copolymers,

do not necessarily represent all the acids which may be 10 propylene/docene-l copolymers and poly-4-methylused: pentene-l.

The molar ratio of acid to alkoxide can be from 1:10 nooon to 20: 1, but preferably the ratio is from 1:1 to 10:1. The total concentration of the two components can be 0.05 to X 10 percent, although in some instances lower and higher concentrations may be used. However, the preferred cont c o 011 centration range is 0.1 to 2.0 percent.

The alkoxide and acid combination may be incorporated X in a number of ways into the polymer. However, preferably the alkoxide is blended first, then the acid is added. O OH (Trans) Excellent results can be obtained by molding a mixture of polymer which contains only the alkoxide with a polymer which contains only the acid. In this method the polymer In the above formulas R represents an alkyl or aralkyl f z are pt i muied b g g Pg' i. at

group of 1 to 12 carbon .atoms and R represents an alkyl {32 some i l ta es p ace i 2? mac "L group containing 3 to 12 carbon carbons atoms, and X b1 E 121mm g mven can represents hydrogen or halogen, en eh into 11t eBpobymers atc wise or COntll UOUS y, In further detail some of the alkoxides and double 3 :35 0t m an my mlxers or compoun mg exil r fs idsgr itiz ir af e which ale useful In the practlce of Since the alkoxides and acids of this invention are dis- Alkoxides persed in a molten state into the molten polymer as already indicated, they should also be compatible with the A1(OC3H7)3 molten polymer at least to the extent of the concentrations Mg(OC H being employed. In addition to having a relatively low Ca(OC H melting point, the acids should be capable of exhibiting a Zn(OC H nematic mesophase as already mentioned. Ti(OC H The alpha-olefin polymers used in the practice of this Zr(OC H invention may have any desired molecular weight rang- Cr[OC(CH3)3]4 ing from materials having inherent viscosities (in tetralin V(OC H- 40 at 145 C.) of 5.0 and above to 0.1 and below. Com- VO(OC H pletely random alpha-olefin copolymers and atactic homo- Na[Zr (OC H-;) polymers which do not crystallize are to be avoided in Mg[Al(OC H the practice of this invention.

A further understanding of our invention will be had K[Al OCH 1 5 from a consideration of the following examples:

4 5 11)4I2 EXAMPLE I Acids Polypropylene (100 g.) having an inherent viscosity (in tetralin at 145 C.) of 1.8 and a conditioned density of 0.909 was blended on hot rolls with 0.2 g. of aluminum (Grimm-goon isopropoxide, then with 0.4 g. of p-tert-butylbenzoic acid. The resulting homogeneous blend was compression 0 molded into a sheet 60 mils thick. The transparency of II the sheet was measured with a Brice-Phoenix photometer (resolution of 10 minutes). The measure of transparency was taken as the ratio of light transmitted at zero degrees 0 with reference to the incident beam I (monochromatic light at 546 m to that transmitted at one degree, 1 higher values of the intensity ratio 1 /1 indicating better transparency. In addition, a sample of the above blend 00011 was injection molded for the measurement of mechanical properties. The following table shows the outstanding C Hn0 transparency and mechanical properties possessed by the treated polypropylene (A) in comparison with a similar CH (CH CH=CH(CH COOH sample of untreated polypropylene (B) and a sample CH (CH CH=CH'CH=CHCOOH treated with a 1% concentration of prior art nucleating CH (CH CH=CHCH=CHCOOH agent aluminum tri-p-tert-butylbenzoate (C).

Polymer Property/Units Test Method Transparency Io/I 15.6 1.09 1.85 Crystallization tempJ" 0.. DTA.-. 144 124 136 Heat distortion tem C 154 154 Tensile yieldlp.s.i. .AS'IM D638... 6,300 5,500 5,600 Stiflness/p.s.i. ASTM D747 200,000 140,000 160,000 Hardness, Rockwell R/seale ASTM D-785.-- km; 081; 00g

Izod impact, notched, 23 C./it.-lb./ln. of notch ASTM 256 Results similar to those in colum (A) were obtained when 0.4 g. of titanium (IV) isopropoxide and 0.5 g. of Property (1) 1r p-n-butoxybenzoic acid were used. All attempts to pre- Denier 29 20 pare completely homogeneous blends of aluminum salts %enaeity,g-/

L37 of substituted benzoic acids were unsuccessful-partiigg ggfl gg g gg gfl g cles were usually visible and the polymer appeared plgmented or smoky.

EXAMPLE II EXAMPLE V A 270 g. sample of a copolymer containing 94% A 1000 g. sample of isotactic polybutene-l having a propylene and 6% ethylene and having an inherent vis- 10 melt index of 2.3 (190 C.; 2.16 kg.) and a melting point cosity of 1.75 was blended in a Banbury mixer with 1.3 of 122 C. (DTA) was blended in a Banbury mixer with of zirconium butoxlde, t f gof p- 10 g. of zinc boron amyloxide, Zn[B(OC H and then heXylbenZOlc acld- A Small disk that w 1 with 2.0 g. of nona-2,4-dienoic acid. The resulting blend Pression molded from i blend had an Intensity fatlo, was molded for physical properties. The results are shown I /I =5.3, compared mm a control value of 1.24. When below, compared with polybutene-l containing no crystalvanadium tetrabutoxide V(OC H was used with p-nli i promote]; propoxybenzoic acid, similar results were obtained, except that the polymer was homogeneously colored a royal blue- Property/Units Polybutene1 EXAMPLE III Test Method Treated Untreated e pronounced t y of ty p y y Hmness, Show D D Dmometen" 68 63 moldings to warp 18 well known. Thus it is necessary, Tensile yield strength/p.s.i ASIM-D-638--. 11,600 9,900 particularly in molding articles that feature broad, flat 1281000 1071000 eat distortion temp./ C 127 120 surfaces, to clamp the mold until crystallization 1s relatively complete. Another well-known characteristic of high-density polyethylene is its poor light transmission, A L even when in the form of relatively thin quenched film. MP E VI A 1000 g. sample of high-density (0.960) polyethylene In accordance with this example several samples of polyhaving a melt index of 4 was blended on the hot rolls allomer and P YP PY 6011131111118 Promoter Combl' (160 C.) with 5.0 g. of p-tert-butylbenzoic acid, then nations within the present invention were processed on with 2.0 g. of aluminum isopropoxide. A 10-mil film was larger scale, commercial size equipment. For comparison molded at 200 C. for two minutes and quenched in water purposes slmllar processing was applied to commercial at 15 C. The intensity ratio I /I of this film was 15.3. polypropylene molding compositions A, B, and C, wh ch The intensity ratio of a IO-mil film of untreated polymer, commercial compositions contained prior art nucleatmg molded in exactly the same manner as above, was 1.4. agents. In further detail, the materials were each molded In order to observe the effect of the additives on the on an Impco injection molder Model HE-300-P1248 ustendency of the polymer to wrap, disks 4 inches in diaming a dishpan mold and a lighter base mold. The dishpan eter were injection molded and allowed to age at room provided specimens for evaluating the clarity of the matemperature for 48 hours. Disks were similarly molded 40 terials and the lighter base provided a thick section for from untreated polymer and aged. Only 16% of the disks evaluating any sinks and voids of the materials. containing the crystallization promoter were warped while The materials were molded at only one condition for 82% of the untreated disks were badly warped. each mold. It is recognized that sinks and voids can be reduced by utilizing optimum molding conditions but no EXAMPLE IV attempt was made to change the molding conditions be- A 1000 g. sample of poly(4-methyl-1-pentene) having tween materials. The conditions utilized represent reasonan I.V. of 1.5 was blended in a small extruder with 3.5 g. able molding conditions for these materials. Table II heof sodium zirconium isopropoxide, Na[Zr (OC H and low sets forth these molding conditions. then with 8.5 g. of p-methoxy-cinnamic acid. The extru- Samples of Tenite polypropylene both treated and undate was chopped and re-extruded through a single-hole treated were evaluated for heat stability. The presence of jet to form a monofilament having essentially no spin the crystallization promoter did not appear to affect the draft. The monofilament was quenched in ice water during heat stability of the polypropylene. spinning and subsequently drafted 12 to 1 over a hot roll Molding results are tabulated in Table I. In this evaluaat 115 C., the properties of this monofilament at 80 C. tion, the pump time (the time during which the maximum are shown in the table below (I) and are compared with a injection pressure is being used) required to bottom the similar monofilament (II) containing no crystallization ram is presented as a measure of the moldability or flow promoter. properties of the samples.

TABLE 1 Flow Rate Pump Time Voids Clarity Tenite Polyallomer 5021 Control 1.7 1:40 None Poor.

Treated. 2.1 1:50 .do Very Good. Tenlte Polyallomer 5B21 Control 1.6 1:40 Medium Poor TreaterL 1.5 1:40 Tenite Polypropylene 4221 Control 2.0 2:00 Treated 2.1 1:30 Tenite Polypropylene 4241 Control. 12.0 1:50 Treated. 12.0 1:15 CommerclalA Control. 3.3 1:25 Do Nucleate 4.8 1:50 Commercial B ontrol 12. 0 1:15 Do Nucleated. 12.0 1:25 Commercial ontrol 4. 8 1:25 Do Nucleated.. 4.0 1:30

TABLE II.-TYPICAL MOLDING CONDITIONS Mold Dishpan Lighter Base Melter Rear, F./ O 400 400 Melter Center, F./ 0...- 450 450 Melter Front, F./ 0.- 450 450 Injector Rear, F./ C 400 400 Nozzle #1 100 160 Nozzle Valve 100 160 Mold Temp., F./ C 50 50 Clamp Timer, sec 15 36 Injection Timer, 5%.. 12 12 Pump Timer, sec.. Gate T er, sec... 9 9 Total Cycle, sec- 36 57 Injector Pressure 1, 000 1,000 Melter Pressure l, 000 1,000 Dwell Pressure 1, 000 1, 000

1 Variable.

The following conclusions may be drawn from these results:

(1) The presence of the crystallization promoters of this invention in the polypropylenes improves their flow properties as measured by pump time, but appears to have little effect on the flow properties of the polyallomers. The flow properties of the commercially avail able nucleated polypropylenes were not improved over those of the corresponding unnucleated materials.

(2) The crystallization promoters of this invention reduce the frequency and size of voids in thick molded articles.

(3) The crystallization promoters of this invention improve the see-through (long range) clarity of the materials.

(4) The crystallization promoters of this invention reduce sinks in thick molded articles.

(5) The heat stability of polypropylene is not impaired by the presence of the crystallization promoters of this invention.

EXAMPLE VII (A) The procedure of Example I above wos followed, except that the polymer was 100 g. of a blend of polymers having the following compositions:

Polymer I.V. Density Parts Polypropylene 1. 8 0. 909 90 Polyethylene 1. 9 0. 956 7 Ethylene/propylene copolymer rubber 2. 5 0. 88 3 In the polymer was blended first 0.22 g. of p-n-butoxybenzoic acid, then 0.28 g. of aluminum isobutoxide. The intensity ratio, I /I of 60-mil sheets molded from this polymer was 7.1, compared with a valve of 1.6 for an untreated sample. Furthermore, the mechanical properties of the treated sample were improved as shown in the following:

Property Treated Untreated Hardness, Rockwell R-scale 172 81 Stiffness, p.s.i 172,000 134, 000 Heat distortion temperature, C 157 146 Property Treated Untreated Hardness, Rockwell R-scale 101 80 t itfuess, p.s .i 163,000 128, 000 Heat distortion temperature, C 151 140 (Q) In a Banbury mixer, 1000 g. of polypropylene having an inherent viscosity of 1.8 and conditioned den- 8 sity of 0.909 was blended first with a mixture of 2.82 g. of magnesium zirconium isopropoxide,

4( 3 '1) 1a and 1.43 g. of sodium zirconium isopropoxlde, NaZr (OC H then with 0.75 g. of p-n-butoxybenzoic acid.

The intensity ratio, 1,,/ 1 of a 60-mil thick sheet molded from this blend was 14.3 compared with 1.09 for the untreated polymer. Other etfects of the additives are shown in the following:

Property Treated Untreated Crystallizationtemperature, C. 142 124 Heat distortion temperature, C 161 154 Stiffness, p.s.i 187, 000 140, 000 Hardness, Rockwell R-soale 101 EXAMPLE VIII In a small glass test tube 0.2 g. of aluminum isopropoxide powder was thoroughly mixed with 0.4 g. of p-tert.- butylbenzoic acid. This mixture was then blended into g. of polypropylene having an inherent viscosity of 1.8 and a conditioned density of 0.909. When this blend was used to compression mold a 60-mil sheet, the sheet contained numerous particles which were clearly visible to the naked eye and many more which were visible with a magnification of 20X. The transparency rating, I /I was 1.67.

It may be seen from the above that our new combination agent of alkoxide-acid readily blends with polyolefin polymer either on a small or large scale. There are no or only minor problems of dispersion or lack of clarity in product as has been encountered in prior art systems. Accordingly, our invention lends itself to the following type applications:

(1) High-density polyethylene having reduced post-mold warpage and better dimensional stability.

(2) Polypropylene having improved clarity, higher stiffness, and higher heat distortion temperature.

(3) Poly(1-butene) having greater stiffness and hardness.

(4) Propylene/ l-butene copolymers with greater rigidity and reduced tack.

(5) Low-viscosity propylene/ l-butene copolymers having a reduced delayed tack time and giving less permeable coatings.

(6) Poly(4-methyl-1-pentene) fibers having improved high-temperature properties.

(7) Polyolefins, in general, having improved moldability (surface finish, uniform mold shrinkage, shorter mold cycle, better mold release) and processability (e.g., chill-roll release).

(8) Propylene/l-butene copolymer film having improved modulus.

In the above examples, the various polyolefins in several instances contained as stabilizers 0.1% concentration of dilauryl 3,3'-thiodipropionate and 0.1% 4,4-butylidenebis (6-tert-butyl-m-cresol). However, other usually used stabilizers may be incorporated.

Although the invention has been described in detail with reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as dlescribed hereinabove and as defined by the appended c aims.

We claim:

1. The process for regulating the crystal development of a polyolefinie composition susceptible of such regulation which comprises blending separately and successively with a melt of said composition the individual components of a multi-component crystallization promoter system comprising (1) one or more metal alkoxides fusible at the blending temperature applied to the polyolefinic composition being processed and (2) one or more organic acids which exhibit either lyotropic or thermotropic mesomorphism at a temperature at least below the melting point of said polyolefinic composition, and solidifying the resulting melt by cooling.

2. The process of claim 1 wherein the poly-alphaolefinic composition has thoroughly dispersed therein an alkoxide-acid promoter combination which is compatible with said composition and which acid component exhibits a liquid crystalline state at a temperature at least below the melting point of said poly-alpha-olefinic composition, said combination being selected from the group consisting of those fusible alkoxides with a formula M(OR) and M[M (OR) wherein M represents a metal with a valence of a, which can have values from 1 to 6 and M represents a metal with a valence of b, which can have a value of 1, 2, or 3 and the acid has the formulas from the groups,

RGH=GH-CH=OHCOOH wherein R represents an alkyl or aralkyl group of 1 to 12 carbon atoms and R represents an alkyl group containing 3 to 12 carbon atom, and X repreent hydrogen or halogen.

3. The process of claim 1 wherein the acid component exhibits a nematic mesophase below the melting point of the polyolefinic composition.

4. Crystallizable poly-alpha-olefinic composition having readily and thoroughly dispersed therein from about 0.05 to about 10.0% by weight of a fusible alkoxide-acid combination crystallization promoter as set forth in claim 2 which is compatible with said composition and which acid component exhibits a liquid crystalline state at a temperature below the melting point of said poly-alphacomposition.

5. The composition of claim 4 wherein the polyolefinic composition substantially completely consists of polypropylene having thoroughly dispersed therein a crystallization promoter which is readily compatible with said polypropylene and essentially comprising a fusible metal alkoxide and an organic acid which exhibits a liquid crystalline state at a temperature at least below the melting point of said polypropylene, the resultant polypropylene having enhanced clarity and improved mechanical propertles.

6. An intermediate combination of at least one metal alkoxide and at least one acid useful as a crystallization promoter in polyolefinic compositions, said combination being further characterized in that the alkoxide is from the group consisting of:

5 11)4]2 and the acid is from the group consisting of JOSEPH L. SCHOFER, Primary Examiner. L. EDELMAN, Assistant Examiner.

U.S. Cl. X.R. 260-882, 94.9, 878 

